The invention concerns a laser spark plug comprising a laser light producing device and a spark plug housing, at whose end towards the combustion chamber there is arranged a coupling-in optical means for coupling laser light into the combustion chamber of an internal combustion engine. The spark plug housing has a fastening region for fastening the laser spark plug in a cylinder head of the internal combustion engine.
The invention further concerns an arrangement including a laser spark plug of the aforementioned kind and a cylinder head having a fixing region for the fastening region of the laser spark plug. Finally, the invention concerns an internal combustion engine, in particular a gas engine, comprising such an arrangement.
Laser ignition is an ignition system which is in an intensive development phase and which has fundamental advantages over conventional spark ignition. One of those advantages is the absence of erosive wear and hot corrosion at the spark plug electrodes, which in conventional electric spark ignition, specifically in relation to the high power density levels of modern gas engines, lead to reduced spark plug service lives and thus considerable operating costs. The increase in the power density of the engine, which is one of the main focuses in engine development, does not represent any difficulty for laser ignition.
Laser ignition to which reference is made in this proposed invention comprises a laser spark plug in which the laser light pulse which lasts only a few nanoseconds is produced with sufficiently high energy. The laser light beams issuing, from for example, a laser crystal are concentrated and focused by way of a suitable optical means and coupled into the combustion chamber by way of a light-transmissive window, the so-called coupling-in optical means or the combustion chamber window, at the end of the laser spark plug, at the combustion chamber side. The plasma spark or ignition spark is produced at the focal point of the laser light beams. The laser ignition system further has an optical pumping device where a quasi-continuous laser light of suitable wavelength is produced. The Laser light is passed by way of a glass fiber cable to the laser crystal in the laser spark plug, and the laser crystal is activated with the laser light until the laser pulse is triggered. To ensure optimum and reliable operation of the laser crystal with the integrated optical interfaces and switches, it is crucial that the temperature of the laser spark plug at the location of installation of the laser crystal is kept as low as possible. In large high-power gas engines, the components delimiting the combustion chamber are subjected to very high thermal loading. Added to that there are often long spark plug shafts in which the spark plugs are fitted and where the wall temperatures are already about 90° C. No higher temperature than a maximum of 130° C. should occur at the laser crystal in operation.
That can be achieved only with difficulty with the geometrical configurations known at the present time of the laser spark plugs, under unfavorable boundary conditions.